Polymer films that are designed to shrink when exposed to heat are useful for many diverse and different applications. Such films, for instance, can be used as packaging materials, binding materials, covering materials, sealing materials, or labeling materials.
When used as a label, for instance, the film may be formed into a tube and then placed around a container. Once placed around the container, the film may be exposed to heat causing the tube to shrink and tightly fit around the container.
In an alternative embodiment, the shrinkable film can be coated with an adhesive and applied to a container. After the container has been used, the container is subjected to heat causing the film to shrink and detach from the container. Once detached, the container can then be cleaned, refilled and reused as desired.
In the past, various different types of films have been proposed for shrink applications. Polyester-based shrink films are particularly advantageous for use on polyester containers, as they facilitate the recycling process by allowing the polyester containers to be reclaimed along with their polyester labels without introducing incompatible resins into the recycling stream. Thus, in the past, polyester polymers have been modified in order to increase their shrink properties. Such polyester films, for instance, are disclosed in U.S. Pat. No. 5,407,752, U.S. Pat. No. 6,630,230, U.S. Pat. No. 6,765,070, U.S. Pat. No. 7,008,698, and U.S. Pat. No. 7,195,822, which are all incorporated herein by reference.
Although the above patents have made great advances in the art, as described above, the polyester polymers were chemically modified or copolymerized with other materials in order to obtain the desired shrink properties.
Various other polymers have also been proposed for use in producing shrinkable films. For instance, in U.S. Pat. No. 6,680,097, which is also incorporated herein by reference, self-adhesive film labels are disclosed containing a stretched film layer, which shrinks when subjected to elevated temperatures. In the '097 patent, polyvinyl chloride is taught as the preferred material used to form the shrinkable film. The '097 patent also discusses using shrinkable polyester films. The polyester films, however, are shown to have less than 10% shrinkage when subjected to a temperature of 80° C. and generally showed a significantly more weakly pronounced longitudinal shrinkage when compared to PVC films.
Various disadvantages, however, may be experienced when attempting to use polyvinyl chloride as a shrinkable film. Polyvinyl chloride resins, for instance, have had problems with heat resistance, weather resistance, chemical resistance, and the like. Polyvinyl chloride films, for instance, are liable to experience the frequent occurrence of fish eye when the film is subjected to printing. Further, problems have also been experienced in properly disposing polyvinyl chloride films, especially when trying to incinerate the films.
In view of the above, a need currently exists for an improved shrinkable film. In particular, a need currently exists for a shrinkable film made from a polyester polymer that does not necessarily have to be modified or combined with other polymers in order to impart desirable shrink properties.